A mold used for making the shape of a hole for manufacturing a hollow part such as a column in general casting is called a core. Casting for manufacturing a hollow cast is made by putting a core into a mold, injecting molten metal into the mold, taking out the cast and the core from the mold after the molten metal hardens, and then separating the core from the cast.
A core or a mold for casting is manufactured, for example, by making molding sand, in which dry sand and a plurality of forming resins are uniformly mulled by a mixer, putting the molding sand into a mold, hardening the molding sand by injecting an amine gas into the molding sand in the mold, and taking out the hardened object.
Such a technique has been disclosed in Korean Patent No. 10-1131033, titled “Use of amine blends for foundry shaped cores and casting metals”. In this related art, phenolic resin and polyisocyanate are used as a forming resin, and molding sand is obtained by mixing the forming resin with sand. The molding sand is hardened at room temperature, using an amine blend as a hardener and a core or a mold made of polyurethane can be obtained through the hardening. This process is called a PUCB (Polyurethane Cold Box) process.
Hardening a core or a mold using an amine gas has various advantages, for example: it can be hardened at room temperature without heating at a high temperature, the hardening speed is higher than high-temperature hardening, and not only the surface of molding sand, but the entirety of the molding sand can be hardened. However, when an amine gas is used as a hardener, a worker may have difficulty in working due to the amine gas odor remaining after hardening or due to an amine gas leak through a gap of a mold.